BRENTWOOD — Newly unsealed documents in the case against Aaron Desjardins, an Epping man who allegedly slit the throat of his ex-wife and set her body on fire to destroy the evidence, reveal he confessed twice to the murder before he was arrested and once while he was in police custody.

Desjardins’ ex-wife, Amanda “Amy” Warf, was killed on the morning of March 7, 2013. Her body was covered in debris and her face was burned beyond recognition when emergency personnel responding to the fire at an abandoned City Concrete building in Exeter found her. She was 36 years old when she died.

According to a supporting affidavit for issuance of search warrants, Desjardins, 37, of 67 Railroad Ave., told his brother-in-law on March 11 during a recorded phone call authorized by the attorney general’s office that he killed Warf. Desjardins said he and Sarah Desjardins, his new wife, decided to kill Warf over custody of his son, William. Warf left Desjardins for another man when she was about four weeks pregnant with the young boy.

During the conversation Desjardins said, “We are monsters,” insisting Sarah planned and helped to execute the killing of Warf.

Court documents indicate Sarah, 35, of 5b Paxton Terrace in Nashua, wanted to be a mother but could not have her own biological children. She spoke to police at length about the custody battle between Desjardins and Warf.

On March 12, Desjardins told Sarah during another recorded phone call that the killing was quick and painless, describing it as “very humane and very fast.” He admitted he slit Warf’s throat and burned her body while Sarah stayed at home to cover up the crime.

When Desjardins was arrested on first-degree murder charges that afternoon he waived his Miranda rights and admitted to the killing, saying he had planned it in advance. Desjardins told the investigators in the months leading up to the murder he intended to pin the death on Warf’s ex-boyfriend or her current live-in boyfriend, Jack Gardner.

Desjardins told police that the former couple had been fighting over William and whether Desjardins could remain on Warf’s health insurance policy.

Desjardins told police he suffered from multiple sclerosis and that he was supposed to stay on Warf’s insurance for three years but a court had recently sided with Warf on the issue. He expressed discontent with the court’s decision.

Desjardins plans to plead insanity as his defense during his upcoming trial, which is scheduled for May 2015. He is facing charges of first-degree murder, conspiracy to commit murder and conspiracy to commit hindering apprehension. Sarah and Desjardins’ sister, Michele Corson, 44, of 373 Water St. in Skowhegan, Maine, are facing conspiracy charges in the case. Corson allegedly brought Desjardins a gun from her home knowing he planned to kill Warf with a knife.

Desjardins reportedly used the weapon to coerce Warf into the plant before killing her.